Rodenticide bait

ABSTRACT

A rodent bait suitable for use on crops comprising a unitary body of intimately mixed particles of metal phosphide such as zinc phosphide, citric acid and a hard wax component. The hard wax component forms a protective coating around the particles of metal phosphide and citric acid. The citric acid has been found to completely decompose the metal phosphide toxicant upon absorption of moisture by the unitary body. Thus, the rodent bait of the invention has the advantage of preventing decomposition of the metal phosphide toxicant until a preset time when it completely decomposes the metal phosphide leaving no toxic residues.

United States Patent [72] Inventor Howard L. Arbaugh Portsmouth, Ohio I2 l 1 Appl. No. 764,941

[22] Filed Oct. 3, 1968 [45] Patented Nov. 30, 1971 [73] Assignee The ARChem Corporation Portsmouth, Ohio [54] RODENTICIDE BAIT 2 Claims, NoDrawings [52] U.S. Cl 424/17, 424/38, 424/128 [51] 1nt.Cl A0ln 11/00[50] Field oi Search 424/17, 38, 128

[56] References Cited UNITED STATES PATENTS 3,132,067 5/1964 Rauscher eta1. 424/38 FOREIGN PATENTS 750,035 5/1933 France 424/17 l ,3 18,597H1963 France 424/128 OTHER REFERENCES Chitty, Control of Rats and Mice,Vol. I, pp. 100- lUI, Oxford at the Clarendo Press, l954.

Primary Examiner-Albert T. Meyers Assistant Examiner-Doris J. Funderburk Attorney-Larson, Taylor and Hinds ABSTRACT: A rodent baitsuitable for use on crops comprising a unitary body ofintimately mixedparticles of metal phosphide such as zinc phosphide, citric acid and ahard wax component. The hard wax component forms a protective coatingaround the particles of metal phosphide and citric acid. The citric acidhas been found to completely decompose the metal phosphide toxicant uponabsorption of moisture by the unitary body. Thus, the rodent bait of theinvention has the advantage of preventing decomposition of the metalphosphide toxicant until a preset time when it completely decomposes themetal phosphide leaving no toxic residues.

RODENTICIDE BAIT This invention is directed to a rodenticide baitcomposition. More particularly, the invention relates to a rodenticidecomposition of the metallic phosphide type which can be used on foodcrops.

No rodenticide has ever been approved for use on food crops in view ofthe obvious toxicity dangers to consumers of food crops treated with therodenticide. Heretofore, rodenticide compositions which are capable ofcompletely decomposing to leave no toxic residues on the crops, yetstable enough to remain acceptable .to the rodents for a sufficientperiod of time, have been unheard of. For example, metallic phosphides,such as zinc phosphide, have been widely used for rat and mouse bait butthey have the drawback of rapidly decomposing when wet or under acidconditions. Although zinc phosphide-cereal baits have been formulatedfor noncrop use, these baits have not been acceptable for oncrop usesince in the absence of moisture the zinc phosphide may be latent in itsrate of decomposition and may cause an unacceptable toxicity tolerancein food crops.

ln view of the unacceptability of rodenticides for oncrop use, it hasbeen necessary, heretofore, to use some form of bait dispenser orstation. Elimination of the need for bait dispensers or stations wouldrepresent a significant savings in time and money to those constantlyconfronted with the problem of rodent control.

It is an object of the invention, therefore, to provide a rodenticidebait composition which prevents the toxicant from decomposing until apredetermined time; yet, when it decomposes, it leaves no toxic residue,a feature which renders the rodenticide bait composition useful on foodcrops.

Another object of the invention is to provide a rodenticide baitcomposition which reduces or substantially eliminates a problem thatplagues all known rodent baits; that is, the problem of spoilage due tomold, dampness, rancidity and sub sequent loss of palatability.

Yet, another object is to prepare a temporarily stabilized rodent baitwhich is universally acceptable by the rodent even under the mostadverse climatic conditions.

A further object is to provide a rodenticide bait which does not requirethe use of a bait dispenser and which can be dropped by aircraft, thrownor broadcast onto the natural habitat of the rodent. A rodenticide baitwhich can be dispensed in this manner eliminates costly dispensers andlarge outlays for manpower for hand-baiting.

These and other objects of the invention are accomplished by arodenticide bait in the form of a unitary body comprising an intimatemixture of particles of metal phosphide, citric acid particles, and awater-insoluble hard wax component, said wax component being uniformlydistributed in said unitary body in the form of a protective coatingover said metal phosphide and citric acid particles. It has beensurprisingly found that citric acid in the rodenticide bait of theinvention acts upon absorption of moisture to completely decompose themetal phosphide on a given schedule. In addition, since many rodentssuch as the Norway, Roof and Polynesian Rat are attracted to citrusfruits, the citric acid enhances the value of the bait.

The metal phosphides, useful in the present invention, are any of themetal phosphides capable of being decomposed by moisture to phosphine.These phosphides are well known in the pesticide art and include, forinstance, the phosphides of alkali metals, alkaline earth metals,aluminum and zinc, nickel, iron and other heavy metals. An especiallyefiective and preferred metal phosphide is zinc phosphide which has beenwidely used for rat and mouse bait.

The metal phosphides, particularly zinc phosphide, have an odorcharacteristic of phosphorus which rodents love. It is preferred,however, to include in the bait composition of the invention, inaddition to the metal phosphide, rodenticide particles of solid foodbaits such as are commonly employed in rodenticide compositions. Themost popular solid food-type baits are the cereals such as corn, wheat,rye, rice, barley, malt, oat groats, peanut hearts or the like animalproteins,

etc., singly or in admixture. Thus, in a preferred embodiment therodenticide composition of the invention comprises an admixture of themetal phosphide, citric acid, and solid food bait, each in particulateform, coated and impregnated with a hard wax component to form awax-bound unitary body.

The wax component employed in the bait composition of the invention maybe any water-insoluble, relatively hard wax or combination of waxes.Illustrative of suitable waxes are parafiin wax, microcrystalline wax,carnabu wax, beeswax, ceresin wax and the like and mixtures thereof. Aparticularly preferred wax component comprises paraffin wax with up toabout 5 percent by weight of ceresin wax based on the combination ofwaxes.

Other ingredients commonly added to rodenticide compositions may also beincluded in the composition of the invention, if desired. These include,for instance, mold inhibitors, flavoring agents and the like.

The concentrations and proportions of wax, metal phosphide and citricacid employed may vary depending upon several factors, for instance, thetime desired for decomposition of the metal phosphide, the presence ofother ingredients, the particular pest target, etc. In all instances,however, the concentration of citric acid should be sufficient to insurecomplete decomposition of the zinc phosphide to zinc oxide. Generally,this concentration of citric acid will fall in the range of about 1 to 4percent by weight based on the metal phosphide which is generallypresent in an amount of about 1 to 2 percent by weight of the totalcomposition. Ordinarily, it is preferred to employ the metal phosphideand citric acid in substantially equal proportions. The amount of waxcomponent employed should be sufficient to uniformly coat and seal theparticles of metal phosphide, citric acid and other components which maybe included in the bait composition; the actual amount being primarilydependent upon the desired time for decomposition of the metalphosphide. In general, the amount of the wax component will fall in therange of about 30 to 40 percent by weight of the total composition.

A particularly preferred rodenticide bait composition of the inventioncomprises, for instance,

1 percent anhydrous-grade citric acidpowdered 1 percent zinc phosphide35 percent microfined paraffin wax-U5. P.-grade, the balance being foodbait particles such as cereals plus stabilized animal proteins.

The rodenticide bait of the invention may be prepared, for instance, byintimately mixing particles of metal phosphide, preferably in powderform, citric acid particles and other ingredients such as solid foodbait in particulate form with the wax component in molten form. Theresulting mixture may be formed into a shaped article by molding,pelleting, tabletting,

etc.

In a preferred method, particles of the metal phosphide together withparticles of solid bait and the wax component are first intimately mixedat a temperature in excess of the melting point of the wax component.The citric acid is then added and the mixing continued at the elevatedtemperature, after which the mixture is extruded and molded intowaxbound and impregnated slugs. This method insures complete binding ofall the ingredients into a slug with each particle coated andimpregnated with the wax component.

The following example is included to further illustrate the presentinvention. In the example, the percentages are based on the total weightof the composition.

EXAMPLE To a mixer equipped with heating means is charged cereal grains,stabilized protein particles and 1 percent technicalgrade zincphosphide. After these components are thoroughly mixed, 35 percentpuremicrofined table-grade paraffin wax and 2 percent microfined ceresin waxare added and the temperature of the mixture is brought to F. withcontinuous stirring. 1 percent anhydrous-grade citric acid is then addedand after thorough mixing, the entire mixture is extruded under apressure of 25,000 psi. through a two-well shoulder design die having anorifice diameter of three-fourths inch, heated to a temperature of 165F. The initial well of the die opens into a second well and is of largerdiameter than the second well. The second well, in turn, opens into aii-inch die channel and is of larger diameter than the channel. Thetotal distance between the entrance to the first well of the die to theorifice is approximately 4 inches. The extrudate is thereby compressedinward and downward in two steps to form a very compact extrudate. Thecompact extrudate is cut into 1%- inch length to provide a wax-bound andimpregnated rodenticide bait slug, three-fourths inch in diameter and linches in length.

It is claimed:

l. A melt extruded slug for rodent control comprising an intimatemixture of about I to 2 percent by weight zinc phosphide particles,about I to 2 percent by weight citric acid particles, about 30 to 40percent by weight of a wax component selected from the group consistingof parafl'm wax and a mixture of paraffin wax and up to about 5 percentby weight of ceresin wax, with the remainder being particles of foodbait, said wax being uniformly distributed in said slug and coating eachof said zinc phosphide, citric acid and food bait particles.

2. A melt extruded slug according to claim 1 comprising about 1 percentby weight zinc phosphide particles, about 35 percent by weight paraffinwax, about 2 percent by weight ceresin wax and about 1 percent by weightcitric acid particles.

i I I! l

2. A melt extruded slug according to claim 1 comprising about 1 percent by weight zinc phosphide particles, about 35 percent by weight paraffin wax, about 2 percent by weight ceresin wax and about 1 percent by weight citric acid particles. 